Effect of chronic exercise and Angiotensin-converting enzyme inhibition on rodent thoracic aorta

Angiotensin converting enzyme inhibition reduces cardiovascular responses to acute stress in myocardially infarcted and chronically stressed rats

Previous studies showed that chronically stressed and myocardially infarcted rats respond with exaggerated cardiovascular responses to acute stress. The present experiments were designed to elucidate whether this effect can be abolished by treatment with the angiotensin converting enzyme (ACE) inhibitor captopril. Sprague Dawley rats were subjected either to sham surgery (Groups 1 and 2) or to myocardial infarction (Groups 3 and 4). The rats of Groups 2 and 4 were also exposed to mild chronic stressing. Four weeks after the operation, mean arterial blood pressure (MABP) and heart rate (HR) were measured under resting conditions and after application of acute stress. The cardiovascular responses to the acute stress were determined again 24 h after administration of captopril orally. Captopril significantly reduced resting MABP in each group. Before administration of captopril, the maximum increases in MABP evoked by the acute stressor in all (infarcted and sham-operated) chronically stressed rats and also in the infarcted nonchronically stressed rats were significantly greater than in the sham-operated rats not exposed to chronic stressing. These differences were abolished by captopril. The results suggest that ACE may improve tolerance of acute stress in heart failure and during chronic stressing.

Optimizing cardiovascular benefits of exercise: a review of rodent models

Although research unanimously maintains that exercise can ward off cardiovascular disease (CVD), the optimal type, duration, intensity, and combination of forms are yet not clear. In our review of existing rodent-based studies on exercise and cardiovascular health, we attempt to find the optimal forms, intensities, and durations of exercise. Using Scopus and Medline, a literature review of English language comparative journal studies of cardiovascular benefits and exercise was performed. This review examines the existing literature on rodent models of aerobic, anaerobic, and power exercise and compares the benefits of various training forms, intensities, and durations. The rodent studies reviewed in this article correlate with reports on human subjects that suggest regular aerobic exercise can improve cardiac and vascular structure and function, as well as lipid profiles, and reduce the risk of CVD. Findings demonstrate an abundance of rodent-based aerobic studies, but a lack of anaerobic and power forms of exercise, as well as comparisons of these three components of exercise. Thus, further studies must be conducted to determine a truly optimal regimen for cardiovascular health.

Propofol increases vascular relaxation in aging rats chronically treated with the angiotensin-converting enzyme inhibitor captopril

BACKGROUND

Both propofol use and advanced age are predictors of intraoperative hypotension. We previously demonstrated that propofol enhances vasodilation in mesenteric arteries from aged rats, partly due to increased nitric oxide (NO) bioavailability. Patients chronically treated with angiotensin-converting enzyme (ACE) inhibitors may exhibit refractory hypotension under general anesthesia. We hypothesized that propofol enhances NO-mediated vasodilation in arteries from aged rats chronically treated with ACE inhibitors.

METHODS

Sprague-Dawley rats aged 12 to 13 months were treated with or without captopril for 7 to 8 weeks, yielding a final age of 14 to 15 months at the time of experimentation. Before euthanasia, arterial blood pressures were obtained through carotid artery cannulation. Concentration-response curves to propofol (0.1-100 µM) or methacholine (MCh) (0.01-3 µM) were then assessed on isolated resistance mesenteric arteries (100-200 μm diameter) from both treatment (captopril) and control rats. MCh relaxation was also assessed after propofol pretreatment (1 and 10 µM). N(G)-nitro-l-arginine methyl ester (l-NAME) (100 µM) and meclofenamate (10 µM) were used to inhibit NO and prostaglandin synthesis, respectively. Concentration-response data were summarized as 50% of the maximum relaxation response or area under the curve.

RESULTS

Mean arterial blood pressure in the captopril-treated rats was lower than in untreated rats (P = 0.049). When comparing relaxation in arteries from captopril-treated versus untreated rats, concentration-response curves revealed that captopril-treated rats display greater direct propofol relaxation (P = 0.018). MCh relaxation in the absence of propofol, however, was not different between captopril-treated and untreated rats (P = 0.80). Propofol pretreatment increased MCh relaxation in arteries from captopril-treated compared with untreated rats (P = 0.029 for 1 µM and P = 0.020 for 10 µM). Meclofenamate did not have an effect in this response (P = 0.22). l-NAME-dependent inhibition of MCh relaxation, however, was greater in arteries from control compared with captopril-treated rats (P = 0.0077). However, propofol increased the proportion of NO-dependent vasodilation to MCh similarly in both groups. This suggests that other vasodilatory pathways are involved in the differential response to MCh in the presence of propofol in captopril-treated rats.

CONCLUSIONS

Our results show that mesenteric arterial relaxation in response to propofol, both by direct stimulation and through modulation of endothelium-dependent mechanisms, is, in part, NO-dependent. In captopril-treated rats, propofol further increased arterial relaxation through a non-NO-dependent vasodilating pathway (e.g., endothelium-derived hyperpolarizing factor), which may account for enhanced vasodilation during propofol exposure in patients treated with ACE inhibitors.

Impaired vascular function in patients with Fontan circulation

BACKGROUND

This study was performed to evaluate the endothelial function in Fontan patients, and to investigate the associated factors which influence the endothelial function in these patients.

METHODS

Flow mediated dilatation (FMD) and nitroglycerin induced dilatation (NG) of the brachial artery, and intima media thickness (IMT) of common carotid artery (CCA) were measured in nonselected Fontan patients (n=44, age 5 to 29 years, median 14 years, 18 females) by means of high-resolution ultrasound according to the standard protocols. The results were compared to age and sex matched controls (n=25, age 5 to 27 years, median 13 years, 10 females).

RESULTS

Fontan patients presented significantly reduced FMD and NG compared with controls (FMD; 6.5+/-2.4 vs. 11.1+/-1.4%, p<0.001, NG; 13.3+/-5.2 vs. 19.4+/-6.2%; p=0.035). Twenty two percent of Fontan patients presented pure endothelial dysfunction, and 34% of patients presented combined endothelial and smooth muscle dysfunction. Although there was no correlation between FMD and IMT, Fontan patients presented increased carotid IMT (0.44+/-0.07 vs. 0.38+/-0.06 mm, p=0.008). In multivariate analysis, duration of exposure to chronic hypoxia was inversely correlated with FMD (p=0.117, hazards ratio=1.294, 95% confidence interval=0.938-1.786). There was higher FMD in patients receiving angiotensin-converting enzyme inhibitors (ACEi) compared with those not receiving ACEi (7.0+/-2.5 vs. 5.5+/-2.2%, p=0.069).

CONCLUSIONS

Endothelial dysfunction is more prevalent in Fontan patients compared with healthy controls, and the previous hypoxia is an independent factor. Although it is not statistically significant, those patients on treatment with ACEi seem to have better endothelial function.